Energy absorption buildup factors of human organs and tissues at energies and penetration depths relevant for radiotherapy and diagnostics

S. R. Manohara,S. M. Hanagodimath,L. Gerward

doi:10.1120/jacmp.v12i4.3557

Abstract

Energy absorption geometric progression (GP) fitting parameters and the corresponding buildup factors have been computed for human organs and tissues, such as adipose tissue, blood (whole), cortical bone, brain (grey/white matter), breast tissue, eye lens, lung tissue, skeletal muscle, ovary, testis, soft tissue, and soft tissue (4‐component), for the photon energy range 0.015–15 MeV and for penetration depths up to 40 mfp (mean free path). The chemical composition of human organs and tissues is seen to influence the energy absorption buildup factors. It is also found that the buildup factor of human organs and tissues changes significantly with the change of incident photon energy and effective atomic number, Zeff. These changes are due to the dominance of different photon interaction processes in different energy regions and different chemical compositions of human organs and tissues.With the proper knowledge of buildup factors of human organs and tissues, energy absorption in the human body can be carefully controlled. The present results will help in estimating safe dose levels for radiotherapy patients and also useful in diagnostics and dosimetry. The tissue‐equivalent materials for skeletal muscle, adipose tissue, cortical bone, and lung tissue are also discussed. It is observed that water and MS20 are good tissue equivalent materials for skeletal muscle in the extended energy range.PACS numbers: 32.80‐t, 87.53‐j, 78.70‐g, 78.70‐Ck

Highlights

297 Manohara et al.: Energy absorption buildup factors of human organs and tissues in which the quantity of interest is the absorbed or deposited energy in the medium considered
We will define tissue equivalence in terms of the effective atomic number, Zeff, which represents a weighted average of the number of electrons per atom in a multi-element material.[5]. Early calculations of Zeff were based on parameterization of the photon interaction cross section by fitting data over limited ranges of energy and atomic number
Values of the Compton partial mass attenuation coefficient, (μ/ρ)Comp, and the total mass attenuation coefficient, (μ/ρ)total, have been obtained for the elements Z = 4–30, and for the human organs and tissues using the WinXCom program.[6,7] The equivalent atomic number, Zeq, for a given human organ or tissue is calculated by matching the ratio, (μ/ρ)Comp /(μ/ρ)total, of that human organ or tissue at a given energy with the corresponding ratio of a pure element at the same energy

Summary

Introduction

297 Manohara et al.: Energy absorption buildup factors of human organs and tissues in which the quantity of interest is the absorbed or deposited energy in the medium considered. There is a need for gamma-ray buildup factors of low-Z complex materials, such as human organs and tissues, in diagnostics, dosimetry, and radiation therapy for absorbed dose estimations. We have calculated geometric progression (GP) fitting parameters and energy absorption buildup factors for human organs and tissues, such as adipose tissue, blood (whole), cortical bone, brain (grey/white matter), breast tissue, eye lens, lung tissue, skeletal muscle, ovary, testis, soft tissue, and soft tissue (4-component) by using the ANSI/ ANS-6.4.3-1991 standard data and the GP fitting formula of Harima et al[9] The calculations have been performed for exposures in the radiotheraptic/diagnostic for gamma (or X-ray) energy range 15 keV–15 MeV up to penetration depths of 40 mfp (mean free path). Data are useful for many applications to medical physicists, especially in radiation therapy and dosimetry, for the construction of phantoms using tissue-equivalent materials

Materials and Methods

Skeletal muscle

Computation of the energy absorption buildup factor

Results & DISCUSSION